Metallic strip is formed into tubing by passing the strip through forming and fin pass rolls deforming the strip into an open tubular shape with the opposing longitudinal edges in close proximity. The strip is then passed through a welding station bonding the longitudinal edges and thus forming a tube.
Subsequent to welding, the tube is typically passed through at least one-set of sizing rolls to form the tube to a desired diameter. The means and apparatus for converting strip to welded tubing is disclosed in U.S. Pat. Nos. 3,700,158 to Schatz et al, 4,697,446 to Yamamoto et al and 4,905,885 to Hellman, Sr., all of which are incorporated in their entirety by reference herein.
In many heat exchanger applications, the walls of the tube are enhanced by providing a textured surface. A variety of enhancement patterns are known to improve the performance of a heat exchange tube. These patterns include corrugated ridges or diamonds as disclosed in U.S. Pat. No. 3,861,462 to McLain and pear shaped grooves as disclosed in U.S. Pat. No. 5,052,476 to Sukumonda et al.
One problem in the manufacture of welded tube is an extruded weld bead. Excess welding material flows from the weld and accumulates on the inner and outer walls of the tube. Removal of the bead generally involves removal of some base material. While the removal of base material is acceptable from non-enhanced (smooth) tube walls, removal from an enhanced surface results in damage to the enhancement pattern in the weld region and decreased tube performance.
One method to remove the weld bead, used primarily in the manufacture of steel tube, is disclosed in U.S. Pat. No. 2,352,306. An oxygen jet is directed against the weld bead soon after welding while the weld bead is hot. The bead ignites resulting in a smooth weld seam. U.S. Pat. No. 4,905,885 discloses a hydraulically controlled bead reduction roller and a backing roller to flatten the weld bead. Another method is the use of cutting tools.
When the walls of the tube are enhanced, the prior art methods of removing the weld bead are unsatisfactory. Mechanical flattening damages the enhancement. A stream of oxygen is deflected by the enhancement and inadequately ignites the weld bead. Cutting destroys a portion of the enhancement pattern.